In radio frequency circuits, such as in the radio frequency transmitters, power amplifiers are commonly used in a circuit block that precedes the antenna. Radio frequency transmitters typically implement, in accordance with the power radiated by the antenna, a mechanism of gain control or of energy saving that acts on the whole transmission chain. An estimate of the power at the output of the power amplifier enables the above-mentioned gain control procedures to be undertaken. To reach a high spectral efficiency in the more recent generation of transmission standards, such as the standard IEEE802.11a/g, CDMA2000, IS95, WCDMA and more, a combination of modulation in amplitude and phase is used. The modulated signal that results is at variable envelope. This category of signals is typically characterised by the ratio between instantaneous peak power and average power. The above-mentioned gain control on the transmission chain operates in accordance with the average power rather than the instantaneous peak power. For these above-mentioned gain controls the use of a detector of peak power is excluded and is not used. Further, it is unnecessary to use a detector for time integrated power or average power.
One known detector of the power of an amplifier in radio frequency is disclosed in the WO 0180421 patent. This patent describes a power amplifier circuit to amplify an input signal. The power amplifier circuit includes an amplification transistor and a circuit for detecting the power. The circuit for detecting power generates a signal that is directly proportional to the level of the power of the amplification transistor. More specifically, the circuit for detecting power generates a direct voltage proportional to the square of a current, where the current is the sum of the radio frequency current and the direct current. This current flows in the amplification transistor and produces an average of the voltage which indicates an accurate power level in the amplification transistor.
Although this power detecting circuit is useful, it is not without its problems and shortcomings. One problem is the power detecting device of an amplifier is very sensitive to temperature. Further this temperature dependency is highly dependent on the idle current of the power amplifier.
Accordingly, a need exists to overcome these problems and shortcomings of the prior art and to provide a device for detecting the power that is not sensitive to temperature and a device that does not depend on the idle current of the power amplifier.